Phytophagous insects are considered prime candidates for ecological speciation because of the often-close connection between their systems of mating and host plant adaptation. Understanding the evolution of traits that pleiotropically couple ecological divergence with reproductive isolation has important implications for the tempo and mode of insect diversification. Life history timing may play an important role in initiating ecological speciation for many species with ephemeral mating seasons. For univoltine insects, divergence in life cycle timing is likely mediated primarily through the regulation of diapause. Here, I will discuss how diapause has played a key role in the adaptive radiation of the Rhagoletis pomonella species complex, and how our current understanding of the evolutionary genetics underlying variation in diapause in these flies suggests that this may be a particularly potent driver of ecological diversification. Not only is diapause regulation capable of imparting strong reproductive isolation, but it appears to be able to evolve rapidly in nature, due in large part to how standing genetic variation influencing diapause development may be maintained in populations.
